For some time toilets comprising an open rim structure have been known, wherein a conventional flush toilet 101 such as the one shown in FIG. 7 comprises a slit opening 134 on a bottom surface of a rim passage 120 in a rim 118 formed over the entire circumference of a toilet main body 102. In this type of open rim structure, flush water supplied from a supply port 106 is supplied from a rim rear water conduit 110 to the rim passage 120, then spouted from the rim passage 120 onto a waste receiving surface 116 through the slit opening 134. The flush toilet 101 with this type of open rim structure has the advantage that it can be manufactured relatively inexpensively but is also subject to the problems described below.
In a conventional flush toilet open rim structure such as that shown, for example, in Patent Document 1 (Japanese Patent No. 4062731), an inside end of a shelf portion in a part reached by flush water immediately after flowing from the rim rear water conduit into the rim portion is made to project further toward the inside than an upper edge of the waste receiving surface, and the slit opening is formed to be narrow. Thus, while one of the flush water stream is circulated clockwise on the shelf portion, and the other flush water stream is circulated counterclockwise on the shelf portion. The flush water circulating clockwise forms a main flow. The main flow makes a U-turn at a front portion of the bowl surface and pushes waste in the direction of a discharge trap. The flush water circulating counter-clockwise on the shelf portion flows into a rear surface portion of the bowl surface in the vicinity of a portion connecting the rim rear water conduit and the rim portion.